Ophthalmologists have developed surgical cataract removal procedures which involve removal of the crystalline lens and replacement with an artificial lens through a small incision in the capsular bag in which the lens material is contained. Charles Kelman and Anton Banko were among the first to successfully develop a technique for removal of cataracts using a handheld surgical instrument with a hollow needle vibrating at ultrasonic frequencies. U.S. Pat. No. 3,589,363 describes their ground-breaking technique. This technique, which has become known as phacoemulsification, involves inserting a needle tip vibrating at ultrasonic frequencies into the eye through a small corneal incision. As the vibrating needle tip and ultrasonic wave contacts the lens material it disintegrates and emulsifies it with an irrigating fluid. A coaxial sleeve over the needle or a second canula delivers the irrigating fluid, and the disintegrated lens disperses to form an emulsion which is aspirated through the hollow interior of the needle.
Depending on the extent of the cataract formation the diseased lens material can vary considerably in hardness and/or density. The harder or more dense the diseased material the more difficult it is to remove using phacoemulsification. Various types of ultrasonic vibration have been tried to improve the rate and efficiency of emulsification; previously using longitudinal alone, but recently using transverse and torsional vibration, as well as combinations thereof. In addition, many have developed alternative needle and tip configurations to try to improve on the standard round needle with a bevelled tip. For example, tips that are flared to produce an “acoustic horn” to focus the ultrasonic sound waves. Yet other examples use transverse steps, or “baffles”, or concave recesses within the mouth of the tip to enhance cavitation and emulsification.
The effect of these tip modifications with transverse or torsional ultrasound is limited because the designs were principally for longitudinal movement of the needle. The standard round tip on a straight needle does not work with torsional ultrasound handpieces, so the bent needle that Kelman developed is used. However this type of bent needle has poor ergonomics and can be difficult to use during phacoemulsification surgery. Because of poor tip efficiency, it is also easily blocked with incompletely emulsified lens material.
The present invention was developed with a view to providing an improved needle tip configuration principally for torsional and transverse ultrasonic handpieces to provide better phacoemulsification efficiency (i.e. puts less energy into the eye, reducing any thermal side effects), especially with a straight needle, whilst maintaining good fluid extraction of emulsified fragments (fluidics). It will be appreciated that the same type of needle tip may also be use for other types of surgical procedure such as removal of tumours (e.g. brain tumours), liposuction, or in dentistry. Therefore the invention is not limited in its application to phacoemulsification.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.